1. Field of the Invention
The present invention relates to an image pickup element for outputting an arbitrary image region and an image pickup device for interpolating an arbitrary image region.
2. Related Background Art
In an image pickup device, to obtain a color image from a single image pickup element, light is incident on the image pickup element through color filter arrays. Color filter arrays are roughly classified into a primary color filter array and a complementary color filter array. In a primary color filter array, three filters, i.e., an R filter for transmitting only red light within the visible light range, a G filter for transmitting only green light within the visible light range, and a B filter for transmitting only blue light within the visible light range are arrayed in, e.g., a matrix. In a complementary color filter array, a cyan (to be referred to as “Cy” hereinafter) filter for shielding only red light within the visible light range, a magenta (to be referred to as “Mg” hereinafter) filter for shielding only green light within the visible light range, and a yellow (to be referred to as “Ye” hereinafter) filter for shielding only blue light within the visible light range are arrayed in, e.g., a matrix. There are various color filter array patterns. FIG. 1 shows an example of the primary color filter array. This is called a Bayer matrix.
The Bayer matrix will be described. Of the basic units of the array pattern of 2×2 color filters, only the upper left pixel can directly output a red signal from a photoelectric conversion element as a detection unit of an image pickup element. Only the upper right and lower left pixels can output a green signal, and only the lower right pixel can output a blue signal. To obtain the respective color signals from these pixels, interpolation processing is required. In interpolation, the value of a pixel to be interpolated is obtained by signal processing or calculation based on the values of the neighboring pixels.
FIGS. 2A to 2C are views for explaining an example of interpolation corresponding to the Bayer matrix shown in FIG. 1. Symbol ◯ indicates an original pixel obtained from a photoelectric conversion element. Symbol Δ indicates an interpolated pixel obtained by interpolation. An arrow indicates the relationship between an interpolated pixel and its original pixel.
FIG. 3 is a block diagram of a conventional single-plate color image pickup device. Referring to FIG. 3, the device comprises a CCD image pickup element 901, an A/D converter (ADC) 902, a memory 903, an interpolation circuit 904, a signal processing circuit 905, and a D/A converter (DAC) 906. The memory 903 requires a capacity corresponding to the number of bits of at least (two lines+two pixels)×ADC. The memory 903 is constituted by, e.g., a FIFO having an output terminal at its middle point.
In the CCD image pickup element 901, a photodetection signal obtained by each photoelectric conversion element is transferred in the vertical direction by a CCD and then transferred in the horizontal direction by a CCD. More specifically, when all photodetection signals of a certain line are transferred by the vertical CCD to reach the horizontal CCD, all the photodetection signals are sequentially transferred in the horizontal direction by the horizonal CCD and output from an output terminal. This operation is sequentially performed for all lines. Therefore, photodetection signals (original pixels) are output from the CCD image pickup element 901 in the order of scanning lines, as shown on the CCD image pickup element 901 in FIG. 3.
Each original pixel output from the CCD image pickup element 901 is A/D-converted by the ADC 902 and stored in the memory 903. A plurality of original pixels on each of the first, second, and third lines output from the memory 903 are input to the interpolation circuit 904. The interpolation circuit 904 interpolates as shown in FIGS. 2A to 2C on the basis of these original pixels and outputs RGB signals interpolated by the interpolated pixels. The signal processing circuit 905 processes the RGB signals by color gain adjustment or edge enhancement. The DAC 906 D/A-converts the processed RGB signals to output analog RGB signals.
In the above-described prior art, interpolated pixels must be obtained on the basis of original pixels output from the CCD image pickup element 901 in the order of scanning lines. For this purpose, the ADC 902, memory 903, and DAC 906 are required in addition to the interpolation circuit 904 and signal processing circuit 905, resulting in an increase in circuit scale.